(a) Technical Field
The present invention relates to a method and system for controlling an electrical vacuum pump, and more particularly, to a method and system for controlling an electrical vacuum pump which prevents generation of peak current and implements a soft start in initial motor starting of the electrical vacuum pump.
(b) Background Art
In general, a brake device of a vehicle starts to decelerate or stop a traveling vehicle and in many passenger vehicles, a hydraulic brake is used, which generates brake force using hydraulic pressure generated by operating a brake pedal. A master cylinder that generates the hydraulic pressure from the hydraulic brake is operated by a force applied by a booster that forms a pressure difference between atmospheric pressure and vacuum pressure based on an engagement amount of the brake pedal.
For the brake booster, an air type is used, which uses pressure provided from a compressor driven by an engine to amplify operation force of the brake pedal and to provide the amplified operation force to a cylinder. Additionally, a vacuum type is widely used, which uses negative pressure of an engine intake manifold. Further, in the general vacuum type brake booster, the negative pressure of the engine intake manifold is used, but a scheme that generates vacuum of the brake booster by applying an electrical vacuum pump (EVP) using an electrical motor may be applied.
The electrical vacuum pump (EVP) is configured to suction air through a negative pressure line by rotating a pump with the electrical motor to generate vacuum in the brake booster connected through the negative pressure line and may be used for secondary vacuum generation to improve a vacuum level of the brake booster in a general engine vehicle capable of using the negative pressure of the engine intake manifold. In particular, in generating the vacuum of the brake booster using the negative pressure of the intake manifold, the electrical vacuum pump of the engine vehicle performs a vacuum supplementation function for a vacuum shortage under a high land driving condition or a turbo charger operating condition.
In particular, for a gasoline engine vehicle, an intake air amount is increased to reduce an exhaust regulation material generated in an initial cold start and since the vacuum level of the brake booster decreases, the electrical vacuum pump is used as the secondary vacuum generating apparatus. Further, when a turbo charger is applied, the vacuum level decreases in the cold start, a high load, and the high land. Therefore, the electrical vacuum pump is used as the secondary vacuum generating apparatus.
In addition, since the vacuum is generated using an atmospheric pressure difference of an intake system in the brake booster, a loss in engine output and fuel efficiency occur due to an intake loss. However, when the electrical vacuum pump is applied, a negative pressure usage of the intake manifold may be minimized, thereby achieving an effect of output and fuel efficiency gains. Further, in an electric vehicle (EV) without the engine or a hybrid electric vehicle (HEV) having a mode in which the engine stops similar to an EV driving mode, the vehicle is driven only by a drive motor.
FIG. 1 shows a diagram exemplifying an operation of an electrical vacuum pump (hereinafter, referred to as ‘EVP’) to which a vane pump type is applied and when a rotor 2 within a casing 1 is rotated using an electric motor, a surge tank of the engine and the brake booster are evacuated while air in the casing is suctioned, closed, transported, and discharged by a vane 3.
Further, a general EVP 10 includes a ground terminal (‘GND’), two controller area network (CAN) communication terminals (‘CAN_HI’ and ‘CAN_LO’), a vacuum sensor terminal, a vehicle power signal terminal (‘IG1’), and six input/output terminals of a source terminal (‘B+’) for driving control as illustrated in FIG. 2. Herein, the CAN communication terminals provide communication between a cluster 30 and an engine management system (EMS) 40, and the EVP 10 is used to display a failure status of the EVP 10 on the cluster 30 (e.g., a display on the cluster) and moreover, used to receive engine on/off status information from the engine management unit (EMS) 40 since the EVP is to be operated in an engine running status.
Further, the vacuum sensor terminal is used for receiving a signal (a vacuum sensor (alternatively, a vacuum switch 21) mounted on the brake booster 20 and when the vacuum sensor outputs a voltage signal depending on a vacuum degree (vacuum pressure) of the brake booster, the vacuum sensor receives the output voltage signal through the vacuum sensor terminal.
Additionally, when the vacuum switch 21 that outputs the signal based on the vacuum degree of the brake booster 20 as an on/off voltage signal is applied, a switch on signal (e.g., voltage signal) is received by force in the switch due to a pressure difference between vacuum pressure and atmospheric pressure. When the vacuum pressure ((−) pressure, that is, negative pressure) of the brake booster 20 is greater than a set level and the difference between the vacuum pressure and the atmospheric pressure is minimal, the vacuum switch 21 is in a switch-on state and when the vacuum pressure is equal to or less than the set level and the difference between the vacuum pressure and the atmospheric pressure is substantial, the vacuum switch 1 is in a switch-off state.
The vehicle power signal terminal (‘IG1’) is a terminal (e.g., signal terminal) used to receive an IG1 state signal and a source terminal (‘B+’) is a terminal used to receive battery constant power (B+). Accordingly, in the related art, the EVP is controlled to be turned on or off according to a logic based on six input/output signals and FIG. 3 is a flowchart illustrating an on/off control process of the EVP according to the related art.
First, as illustrated in FIG. 3, while the B+ constant power (B+ source) is connected to receive drive power (S1), an IG1 signal is received (S2) and when an engine on signal (IG2 signal) is received (S3), where pressure P of the brake booster detected by the vacuum sensor is greater than set vacuum pressure (Pv, e.g., about −250 mmHg), the EVP is turned on (S4 and S5).
Subsequently, when a set operation time (Ton) elapses, the EVP is turned off (S6 and S7). When the vacuum switch is applied, and the vacuum switch is in the switch-on state, the EVP is turned on and when the vacuum switch is in the switch-off state, the EVP is turned off. Meanwhile, when a pump driving motor is started while the EVP is turned on, high start current flows in an initial stage and FIG. 4 illustrates start current at the moment when the motor starts while switching on the vacuum switch.
As illustrated in FIG. 4, after the switch is turned on, a substantial current load is generated while starting the motor of the EVP and start current is illustrated in a peak current form, and as a result, momentary voltage drop of the vehicle power may occur and noise may be generated. In other words, when the vehicle is driven or a system (e.g., an in-vehicle controller, and the like) sharing power is operated in an initial load state in which the start current is loaded, a start time increases and the peak current during the starting of the motor increases and the momentary voltage drop of the vehicle power influences another system using the vehicle power and causes the noise generation.
Accordingly, the source terminal (B+) of the EVP is wired with separate battery constant power to minimize the vehicle load and a hardware filter circuit is applied to suppress the noise generation and limit the start current as illustrated in FIG. 5. In the circuit of FIG. 5, ‘+V’ represents battery voltage, ‘Vout’ represents filter output voltage (e.g., EVP input voltage) applied to the EVP, and reference numeral U1 represents a regulator.
When battery power is applied through the regulator U1, a capacitor C2 is discharged, and as a result, a switch Q1 operates and thus, output voltage applied to the EVP is in a low voltage state (e.g., about 1.2 V). Subsequently, when the output voltage increases while charging the capacitor C2, and as a result, the capacitor C2 is completely charged, the output voltage applied to the EVP increases substantially to remove the peak current generated during the starting. In particular, an output voltage increase time is adjusted by time constants of the capacitor C2 and a resistor R3.
However, technology to which a hardware filter is applied has a disadvantage of an increase in cost and an increase of circuit complexity due to a hardware configuration and since the time constants are determined by an output resistance value of power, linear control may be difficult. Further, the illustrated hardware filter as a noise removal filter in which an attenuation area for the peak current is fixed and patterned may not remove various load peaks caused by a vehicle environment.
The above information disclosed in this section is merely for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.